340 A. T. MASTERMAN. 



PART II. 

 On the Structure of Cephalodiscus dodecalophus, Mcintosh. 



As already indicated in the previous work upon Ac tin o- 

 trocha, the comparison of some of its organs with those of 

 Balanoglossus indicated that a renewed study of Cephalo- 

 discus and its ^^notochord" was desirable. The work here 

 referred to was done upon material from the "Challenger" 

 collection. 



The former work upon Cephalodiscus is confined to a 

 description of the chief anatomical features by Professor 

 Mcintosh (2) in the " Challenger" series, and an appendix to 

 it by Mr. S. F. Harmer (1), the principal feature of which is 

 a detailed comparison of this species with Balanoglossus, 

 as a result of which the group Hemichorda has by many 

 been made to include these two species in addition to Rhab- 

 dopleura. 



As already mentioned in the preceding paper on Actino- 

 trocha, work on this animal and considerations leading there- 

 from caused me to suspect the presence in Cephalodiscus 

 of a notochord different in form and position from that already 

 described as such by Harmer. I must here express a deep 

 sense of gratitude to Professor Mcintosh, LL.D., F.Il.S., for 

 the gift of specimens of this unique animal, taken from the 

 few now remaining in his hands. I hope to be able to publish 

 later the results of labour upon the buds and young forms, but 

 this note must be confined to the description of some organs 

 not hitherto noticed, and to the inferences to be drawn there- 

 from. It need only be mentioned that my pre-conceived view 

 that Harmer^s " notochord " is the homologue of the subneural 

 gland, and that Cephalodiscus has a paired notochord, has 

 been confirmed to a remarkable degree. 



